In June 1941, the Coolidge went into service with the American Army as a transport ship for reinforcing garrisons in the Pacific. A few months later the Japanese attacked Pearl Harbor on December 7, 1941. After this, the Coolidge was stripped of her finery, painted gun-metal grey, mounted with guns and turned into a troop ship. Many of the fixtures and fittings were removed or boarded up for protection. After full conversion in 1942, she could carry over 5000 troops.

A large military base and harbour had been established on Espiritu Santo and the harbour was heavily protected by mines. Information about safe entry into the harbour had been accidentally omitted from the Coolidge's sailing orders, and upon her approach to Santo on October 26, 1942, the SS Coolidge, fearing Japanese submarines and unaware of the mine fields, attempted to enter the harbour through the largest and most obvious channel. A friendly mine struck the ship at the engine room and moments later, a second mine hit her near the stern.

Captain Henry Nelson, knowing that he was going to lose the ship, ran her aground and ordered troops to abandon ship. Not believing the ship would sink, troops were told to leave all of their belongings behind under the impression that they would conduct salvage operations over the next few days.

Over the course of the next 90 minutes, 5,340 men got safely off of the wreck and to shore. There was no panic as the troops disembarked - many even walked to shore. However, the captain's attempts to beach the ship were unsuccessful due to the coral reef. The Coolidge listed heavily on her side, sank, and slid down the slope into the channel. She now rests on her port side with her bow at a depth of 20 metres (70 ft) and her stern at 70 metres (240 ft).

The SS President Coolidge is one of the best dive sites in Vanuatu and the world attracting thousands each year into Espiritu Santo.